The production of petroleum coke from the residuum portion of petroleum crude oil is a common operation in most crude oil refineries. The manufacture of petroleum coke is generally accomplished by placing heated residuum into large vertical vessels termed "coke drums," and allowing the residuum to stand (in the absence of air) for several hours. The residuum slowly solidifies into a mostly carbonatious solid material. In the process, additional hydrocarbonatious materials are driven off and recovered. At the end of the cycle, the coke drum is filled with a generally solid, albeit porous, mass of petroleum coke.
After solidification, the coke must be removed from the coke drum. This is generally accomplished by injecting water into the bottom of the coke drum while the coke is still hot. Much of the water flashes to steam which rises upwardly through the porous mass of coke.
In the present-day method of injecting water into the coke drum, a very high rate of water is initially injected. This is commonly called "proofing." Almost immediately thereafter, the injection rate is reduced to a smaller flow rate, but then the flow rate is steadily increased ("ramped up") from this smaller flow rate throughout the initial first hour of water injection.
It has been found, however, that present-day methods of injecting water into the hot coke severely stresses the steel shell of the coke drum. Such stressing causes metal fatigue and eventual failure of the coke drum.
Accordingly, there is a need for a method for cooling petroleum coke in a petroleum coke drum which is less stressful to the coke drum than are prior art methods.